Hose clamps of the type specified are of course very well known, the clamp being tightened or loosened by rotation of the worm screw in the respective direction, such rotation moving the tang to increase or decrease its degree of overlap with the remainder of the metal band and hence the periphery of the clamp.
When the rack is provided by grooves that do not penetrate the band it is difficult to achieve the necessary high clamping pressures. Moreover, the grooves tend to wear easily with use and after a short time slipping can occur as the clamp is tightened.
Two major problems arise when the rack is provided by slots that penetrate completely through the band. Theoretically the depth of the worm screw lands could be made just equal to the thickness of the band, so as to have the maximum bearing surface without protrusion from the other side of the slot. In industrial practice this would require uneconomically precise tolerances, and there is a tendency therefore to provide for a deeper land, to ensure that the clamp can provide the necessary clamping pressure when tightened. Another problem is that some hose materials, especially silicone rubber materials, tend to extrude through the slots on tightening the clamp about the article being clamped. Such extrusion not only damages the hose but also tends to cause the clamp to stick and be difficult to loosen again when necessary.
At least two prior art clamps of the slotted type are being produced having shields between the band and the clamped article to prevent these problems. In one of these prior art clamps, slots are only provided over a predetermined distance to give a recommended range of diameters for the clamp, while the screw and its housing are set back from the other end of the band by a corresponding distance. Thus, an extended unslotted portion of the tang is interposed between the slotted portion and the clamped article when the clamp is in position; this arrangement is wasteful in material. Moreover, this extended unslotted tang portion must move under the remainder of the band while it is tight against the clamped article and tends to scrape the surface of the article. In addition, the range of adjustment is limited, since the extended unslotted tang portion will eventually complete a circle and butt against the housing.
A second prior art shielded clamp has an unslotted extra tang member welded to the inner surface of the band so as to pass behind the screw housing and the slots; this is subject to the same disadvantages as the first-described extended tang clamp.